1. Field of Invention
The present invention relates to a lock comprising a lock core and lock sleeve, and more particular to a lock enhancing device disposed in relation with the lock core and lock sleeve for enhancing the structural resistance for the lock core against an axial force for pulling the lock core out of the lock sleeve.
2. Description of Related Arts
A lock is widely used in houses, vehicles, cabinets, drawers and security boxes for safety purposes. Many types of locks, such as key-type locks, secret-code-type locks and electric-signal-triggered locks, have been developed to satisfy various needs. Among them, the key-type locks remain the most commonly adopted kind for their inexpensive costs and ease of installation. They may be readily found in houses, offices and other facilities.
A traditional key-type lock is basically composed of a lock core, lock sleeve and transmission lever. The lock core includes a key receptacle for receiving the key therein. The lock sleeve has a set of tumbler barrels communicating with the key receptacle as the lock core is inserted into the lock sleeve. Pressure springs and tumblers are disposed in the tumbler barrels to form a secret code that would block the relative rotation movement between the lock core and lock sleeve, when no key or an incorrect key is inserted into the key receptacle. Yet, when the correct key is inserted, the teeth of the key will push the tumblers to a position that allows the lock core to rotate with respect to the lock sleeve. The transmission lever is connected to the lock core in such a manner when the correct key turns the lock core to rotate, it accordingly drives the transmission lever to rotate in order to active a lock bolt to a lock or unlock position. Such lock can be found, for example, in U.S. Pat. No. 2,814,941 entitled “Lock Core” to Frank Ellison Best on Dec. 3, 1957.
One drawback of the abovementioned lock is its structural weakness in resisting an axial force that is applied to pull the lock core out of the lock sleeve. The lock core is externally threaded at its end in correspondence with a cap nut that is internally threaded. The nut cap has an inner diameter smaller than that of the lock sleeve and an outer diameter greater than the same so that when it engages the lock core received in the lock sleeve, it blocks the axial movement of the lock core with respect to the lock sleeve. However, the engagement of the cap nut and lock cores provides limited restraint to their relative axial movement. A rather great force may be able to pull the lock core out of the lock sleeve and render the lock ineffective.
Although the tumblers help resist against the axial force for pulling the lock core out of the lock sleeve, they may yield in certain circumstances. Because the tumblers are retained in the tumbler barrels with pressure springs, they can move along the barrels by pressing the springs and release the lock core to rotate with respect to the lock sleeve—an action usually happens when a correct key is inserted into the key receptacle. However, this may happen when an exceptional large axial force is applied to pull to lock core out of the lock sleeve. When the axial force is large enough, the interface between the lock core and tumbler barrels may deform. As a result, the tumblers may be pushed upward along the tumbler barrels and finally give way to the axial force.
In order to cope with this issue, the Builders Hardware Manufacturers Association (BHMA) accredited by the American National Standards Institution (ANSI) has develop a standard for lock core in resisting the axial force to remain structural integrity. The standard defines three classes: the third class is 2300N resistance; the second class is 4800N resistance; and the first class is 11000N resistance. Of course, the lock passes the tests of the first class resistance is safer than the ones passing the tests of lower classes in terms of resisting the axial force that is applied to pull the lock core out of the lock sleeve.